Analysis of Italian seismicity by using a nonextensive approach

Using the INGV (National Institute of Geophysics and Volcanology) seismic catalogue, nonextensive analysis of the instrumental seismicity of Italy was performed. The time span of the analyzed catalogue is from April 16, 2005 to March 31, 2009, and only events with magnitude ML ≥ 1.9 were considered. The analysis of the spatial variation of the nonextensive parameters q and a was performed by means of scanning the Italian territory by a 1° × 1° spatial window, with a shift of 0.2° in longitude and latitude. The nonextensive parameters were estimated by means of the Levenberg–Marquadt nonlinear least square fitting method, and the obtained results were checked for stability with the variation of a0 and q0, the initial values of the parameters in the fitting procedure. It was found that the q value is relatively low in areas, in which the strongest events (Mw > 5.5 during the last 40 years) occurred. This finding could suggest that different earthquake triggering mechanisms govern the Italian seismicity, stick–slip-like where q is relatively low and fragment-asperity interaction-type where q is relatively high. Of course new analyses from different areas are needed in order to test such findings.

Research Highlights► Nonextensivity is a consistent theoretical framework for investigating seismicity. ► Italian seismicity shows a quasi-homogenous spatial distribution of the parameter a. ► Italian seismicity shows a patchy spatial variation of the parameter q. ► The parameter q could indicate different earthquake triggering mechanisms.